Jay: Your timeline is right on; you nailed it.
Time actually spent in field service 1 hour maybe.
One hour's a stretch and this is precisely the reason so many JWs still go out in service. It doesn't require much, nothing bad's going to happen, and there's a payback. It's a waste of time, sure, but no more so than going to work at a job where you aren't required to do much. It fills the time, and you get paid. FS is the same way; the paycheck is psychological; you are relieved from guilt.
Your timeline left 35-55 minutes open for actual field service, but even THAT may be too liberal. Most of that time is spent standing in front of the door of an empty house, bookbags in hand, chatting about mundane things and whiling away the moments, followed by the slow shuffle to the next door while hoping no one's home there, either. On the rare occasion someone answers, the conversation is brief: not interested, thanks, close door. Next thing you know you're at the end of the block and there's a crowd of witnesses surrounding the car, impatiently waiting to move on to someplace with coffee and food.
As for those return visits from 11:30 to 12:00? Phantom service. "We're going to make some calls" is the JW equivalent of "have a nice day."